The only thing that differentiates 180° review from 90° one is self-review - it adds a few new options in properties.
Time restrictions allow you to set the time period for the whole review and for the self-review.
In details you can decide if the self-review is mandatory or optional.
When creating a page, you can choose whether it will be visible for the supervisor, employee or both.
Also, when adding a question, you can create alternative content for the supervisor that will be visible for them instead of the initial content.
Apart from those few details, creating a 180° review works the same as creating the 90° one.